dmaengine: mv_xor_v2: remove unnecessary write to DESQ_STOP register

Remove unnecessary write to DESQ_STOP register, this register is used to
enable or disable the XOR engine, and not to issue all pending
descriptors in the queue. mv_xor_v2 driver already writes to this
register and enable XOR engine in the mv_xor_v2_descq_init() function,
called during initialization.

Signed-off-by: Hanna Hawa <hannah@marvell.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>